The study, conducted by researchers at Columbia University’s Mailman School of Public Health and the Rutgers School of Public Health, followed 193 men between the ages of 38 and 49 from 2005 through 2008. Participants took tests that measured stress in their work and lives on both a subjective (how they felt overall) and objective (actual events causing the stress) scale. They also provided semen samples for the research each time.

The participant samples were tested using standard fertility methods assessing the concentration, motility and appearance of sperm. What they found was that psychological stress is harmful to the quality of sperm and semen, and decreases its ability to fertilize an egg.

“Men who feel stressed are more likely to have lower concentrations of sperm in their ejaculate, and the sperm they have are more likely to be misshapen or have impaired motility,” according to senior study author Pam Factor-Litvak, PhD, an associate professor of epidemiology at the Mailman School. “These deficits could be associated with fertility problems."

The study found that, both subjectively and objectively, life stress degraded semen quality, even when health issues were accounted for. Even though men with job strain have diminished levels of testosterone, workplace stress was not a factor in the study. However, unemployed men did have lower-quality sperm than employed participants, no matter what their other levels of stress.

“Stress has long been identified as having an influence on health. Our research suggests that men’s reproductive health may also be affected by their social environment,” said Teresa Janevic, PhD, the study’s first author and assistant professor at the Rutgers School of Public Health.